Storage apparatuses that comprise a plurality of disk devices have been known for some time. In a storage apparatus, for example, a plurality of disk devices configures a logical unit, and a host computer or the like can access the logical unit. The problem is that if all the disk devices in a storage apparatus like this are designed so as to be access-enabled at all times, power consumption will be high.
Accordingly, technology for transitioning to a power-saving mode, for example, by spinning down the group of disk devices (stopping the disks) of a non-accessed logical unit when there has been no access from the host computer or the like for a prescribed period of time is known (Refer to Japanese Patent Laid-open No. 2000-293314).
Thus, when an access occurs while the group of disk devices is in the power-saving mode, for example, all of the disk devices of the group of disk devices are started up. In this case, a large amount of power can be needed to start up all the disk devices. In order to cope with this, either a high-capacity power source capable of supplying this power must be provided in the storage apparatus, or control for starting up the disk devices consecutively using the power capable of being supplied by the power source must be carried out.
Providing a high-capacity power source makes it possible to startup a large number of disk devices, but since the power used at startup is not required at times other than startup, the power source suffers from low utilization efficiency. Further, providing a high-capacity power source also leads to such problems as high storage apparatus manufacturing costs, and the need to secure a larger installation site. Meanwhile, carrying out control for consecutively starting up the disk devices raises the problem of not being able to respond to an access attempt from the host computer until all the disk devices have been started up, thereby lowering responsiveness and causing the host computer to time out.
Furthermore, technology for calculating and booting up the maximum number of devices capable of being booted up based on power supply capabilities is known as control for starting up a group of disk devices using the power that the power source is capable of supplying at times unrelated to host computer access (Refer to Japanese Patent Laid-open No. 2000-10678). Japanese Patent Laid-open No. 2000-10678 relates to booting up a device at times unrelated to an access attempt from the host computer, and does not give any consideration at all to responsiveness to a host computer access.
Meanwhile, as a technique for responding quickly to an access from the host computer while reducing power consumption, technology that sets the number of disk devices corresponding to the redundancy of a logical volume configured as a RAID (Redundant Array of Inexpensive Disks) group to the power-saving mode is known (Refer to Japanese Patent Laid-open No. 2005-228288).